‘These areas are made to burn’: When it comes to the health of the forests surrounding Boulder, there is no replacement for fire

Since the end of the 19th century, there has been a divide in how humans see nature. John Muir (naturalist, essayist, and founder of the Sierra Club) was one of the early adopters of a biocentric view: that humans are not more important than the world around them. Muir believed large swaths of nature should be left alone to evolve and change without human manipulation.

“None of Nature’s landscapes are ugly so long as they are wild,” Muir wrote in 1901.

Conversely, Gifford Pinchot (the first chief of the U.S. Forest Service and close collaborator with Theodore Roosevelt in the president’s conservation efforts) saw nature through an anthropocentric lens: that nature’s value depends on its utility to humans.

“Conservation means the wise use of the earth and its resources for the lasting good of men,” Gifford wrote in 1947.

Today, many people recognize validity within both these arguments. Marrying the two, however, requires squaring that pesky, proverbial circle. How do we get what we want from nature while also giving nature what it needs? Forest management around Boulder does not escape this paradox. 

“A prescription for forest health may look different than one purely for [reduced] fire risk,” said Chris Wanner, Boulder’s vegetation stewardship senior manager. 

Wanner works for the Open Space and Mountain Parks (OSMP) division of the city, which collaborates with wildland chief Brian Oliver and the rest of the Boulder Fire-Rescue Department to assess, and address, fire risk around town. But while the fire department’s priority is protecting human homes, Wanner’s job is to advocate for the ecosystems and animals that can’t advocate for themselves. 

“These are fire-adapted ecosystems,” Wanner said of the 45,000 acres of city-owned open space around Boulder. “Over the millennia there have been regular return intervals of fire. Over the past 100-150 years we’ve gotten really good at putting fires out, taking that natural piece out of the ecosystem.”

Historically, ponderosa pine ecosystems burned every 10-20 years, with larger fires coming through every 30-60 years. In the 100-150 years humans have been suppressing fire, the landscape around Boulder has missed multiple fire cycles. One of the ramifications of these missed cycles is a buildup of fuels. In fire-adapted landscapes, fire plays a leading role in decomposition and nutrient cycling. Without fire, fallen trees and smaller debris remain on the ground, accumulating. And reduced moisture from a changing climate means those added fuels are almost always primed to ignite.

Wanner spoke of the needles dropped from ponderosa pines. These needles, when not burned with any sort of frequency, dampen the growth of other members of the forest. “It acts like mulch in your yard,” Wanner said. “It’s inhibiting the growth of the understory, so you’re not getting the diversity and the cover of other native plant species.”

This lack of an understory that would normally include native grasses and shrubs ripples up the food chain, affecting wildlife that populate the area. Foraging turkeys and elk are left hungry, since dry needles aren’t as palatable as fresh, grassy greens.

“Not only do you have the increased litter cover, but you’ve also got many more trees and much higher shade cover,” Wanner said. “So you’ve got this competition between overstory trees and vegetation that would normally grow underneath.”

‘These areas are made to burn, and they will burn”

Unlike “stand-replacing crown fires,” which are typical in lodge-pole pine forests, ponderosa forests are adapted to more frequent, cooler ground fires that clear away the finer fuels and burn off many younger ponderosa pines — keeping the forests open and park-like. (“Crown fire” means the fire burns all the way to the top of the tree, likely killing the tree. “Stand replacing” means most trees in the fire will be killed.)

“If you walk up on Shanahan, the trees are nice and open-spaced, 15 to 20 feet apart,” Wanner said. “You have some trees, but it’s not so much that it’s shading out all of the ground.

“We can mimic some of that with [mechanical] thinning. You can go in and take some of the trees out which will give you less competition, more sunlight, more resources to the ground. But really the only way to address the fine fuels, like the needles and dead grasses, is through fire.”

Fire also keeps nutrients in the landscape. When you cut down a tree and take it from the forest, the nutrients within the tree are gone from the ecosystem. A burned tree, however, left where it died, will eventually leach its goods back into the soil. And in the meantime, the snag (a standing dead tree) will become a luxurious home for some lucky small mammal. “All kinds of critters use those dead, rotten trees for habitat,” Wanner said.

Another means of mitigation used by the city is cattle grazing. But again, while this has benefits to humans in terms of fire reduction, it isn’t the healthiest for the forest. Wanner acknowledged that cattle do away with some of the finer fuels, such as the grasses. Yet it seems cattle are about as enthusiastic about eating dead pine needles as elk and turkeys are. 

In the end, for the health of the forests surrounding Boulder, there is no replacement for fire. That conclusion might be easier to stomach if our homes weren’t so near those forests. But if John Muir were alive, he would probably remind us that nature does not place humans above other beings, and we’d do well to check our hubris. As he wrote in 1867: 

“The world, we are told, was made especially for man — a presumption not supported by all the facts. A numerous class of men are painfully astonished whenever they find anything, living or dead, in all God’s universe, which they cannot eat or render in some way what they call useful to themselves.”

The forests surrounding Boulder need something we don’t necessarily want them to have. But in the end, the ecosystem will self-correct — with or without our blessing.

“These are fire-adapted ecosystems,” Wanner reiterated. “We can make them more resilient and decrease some of the intensity of a fire, but these areas are made to burn, and they will burn.”